Design mode on a form of a MainWindow (derived from QMainWindow) does not allow one (in any way I can see) to add a tool button to a tool bar that has been added to the main window.
If I try drag and drop from the widgets panel, I get a "Not allowed" symbol (on Linux, behavior similar on Mac) - I can't drop the tool button on to the tool bar (I took a screenshot, but it is not informative because the "Not allowed" cursor symbol is not shown in the screenshot).
If I right-click on the tool bar, the context menu that pops up has options to append a separator, promote the QToolBar, or remove the tool bar. No option to add a tool button.
I have a pretty good idea of how I could add a QToolButton programmatically (unless I misunderstand how QToolBar is supposed to work), but I would prefer that I understand how to use design mode properly.
Thanks for any help.
For adding one tool button to toolBar you should :